This invention relates to deactivators and, in particular, to deactivators for use in deactivating the magnetic tags or labels used in an electronic article surveillance ("EAS") system.
A type of magnetic tag or label used in an EAS system contains a control element formed of a magnetically semi-hard material. The state of the magnetic tag or label, as detected by an exit interrogation system, is determined in accordance with the magnetized state of the control element.
In some types of EAS systems, the tag or label is active when the control element is magnetized along a certain dimension. Thus, in these types of systems, the tag or label is deactivated by demagnetizing the control element or by substantially changing the magnetization state as by imprinting a multipole pattern. The tag or element can then be reactivated by magnetizing the element.
In order to deactivate these magnetic tags or labels, a variety of deactivators have been developed. One such deactivator is manufactured under the number ZK151 by the assignee of the present application and is shown in FIG. 1. This deactivator comprises a main linear multipole magnet 101 formed from alternating polarity magnetic strips 101A-101H. These strips are adjacently arranged along the width of the deactivator and extend along its length, with the alternating polarities being shown as the conventional north N and south S magnetic polarities.
Two subsidiary multipole magnets 102 and 103 are also provided in the deactivator. These subsidiary multipole magnets are situated along the lengths of opposing sides of the main multipole magnet 101 and have alternating polarity adjacently arranged magnetic elements 102A and 103A, respectively. The widths of these elements are equal to the widths of the elements 101A to 101H.
Using the aforesaid deactivator, successful deactivation of a tag or label depends on the orientation of the tag or label when moved across the deactivator. If a tag or label has its length along the width of the deactivator and is moved along its length, there is a high likelihood of successful deactivation. Also a tag with its length along the length of the deactivator, which is moved along the deactivator width and past its side will also have a high likelihood of deactivation. As the tag orientation and movement deviate from these two situations, successful deactivation becomes less likely. This is especially true for narrow tags or labels moved with their lengths along the length or width of the deactivator and whose widths are equal to or less than the multipole magnetic spacing.
Another type of deactivator which has less sensitivity to tag or label orientation is disclosed in U.S. Pat. No. 4,684,930 to Minasy, et al. The deactivator of the Minasy, et al. patent comprises two linear multipole magnets arranged in parallel planes. Each magnet has magnetic strips of alternating polarity arranged along the width of the magnet and extending along its length. These magnets are further arranged with their lengths orthogonal to each other and wrapped around a rotatable cylinder.
The aforesaid construction of the deactivator of the Minasy, et al. patent makes the deactivator less sensitive to tag or label orientation or movement direction. However, the need to use two multipole magnets and to situate them in orthogonal planes and on a roller, complicates the manufacturing of the deactivator.
Also, when similar strength magnet material is used for the two magnets, the surface field pattern is such that the top multipole magnet dominates and has the higher field levels. Matching the materials such that the surface field levels caused by the two magnets are equal is very difficult. Also, since the field falloff vs. height curves are nonlinear, matching the surface field levels would not be sufficient to cause the field levels at 1 mm or 2 mm above the surface to be matched. Therefore, performance suffers.
It is, therefore, an object of the present invention to provide an improved deactivator for magnetic EAS tags or labels which has decreased sensitivity to tag or label orientation.
It is a further object of the present invention to provide a deactivator of the aforementioned type which is of simplified construction and easy to use.